It is strange, when i use some theme-detector in any of the websites I’ve done with generatepress, always it appears the the parent theme.
Logically I customizing the theme name, author, etc. in child theme style.css.
It’s most likely just the algorithm those websites are using to test for the theme – instead of detecting the child theme they’re looking for the parent theme.
It’s something those sites would have to add into their code.